Congenital Adrenal Hyperplasia (CAH)

Congenital adrenal hyperplasia (CAH) is a group of inherited conditions that affect how the adrenal glands make certain hormones. Because of a missing or reduced enzyme, the glands struggle to make cortisol and sometimes aldosterone, while often making more androgens. It is present from birth, identified through hormone testing, and generally managed long term with a clinician.

What congenital adrenal hyperplasia is

The adrenal glands, which sit above the kidneys, produce several hormones, including cortisol (which helps the body handle stress and regulate many processes), aldosterone (which helps balance salt and fluids), and androgens. Making these hormones depends on a series of enzymes. In CAH, an inherited change reduces one of these enzymes, most commonly one called 21-hydroxylase. As a result, cortisol production is limited, and the building blocks that would have been used are diverted toward making more androgens.

Because cortisol is low, the pituitary sends more of its stimulating signal to the adrenal glands, which causes them to enlarge — the "hyperplasia" in the name. CAH ranges from more severe forms recognised early in life to milder forms that may not be noticed until later. For background on the relevant hormones, see our hormones section, and the related adrenal topics.

Common signs and symptoms

Signs depend on the form and severity, and on whether salt and fluid balance is affected. They may include:

• In more severe forms recognised early, signs related to low cortisol and disturbed salt and fluid balance, which can be serious
• Differences in genital appearance noticed at birth in some cases
• Early signs of puberty or rapid early growth
• In milder forms appearing later, features such as irregular periods, excess body or facial hair, or acne
• Fertility-related concerns in some people

Milder forms can resemble other hormonal conditions, while more severe forms are often picked up in early life, sometimes through newborn screening where it is offered.

What causes it

CAH is caused by inherited changes in the genes that provide instructions for the adrenal enzymes, most often the enzyme 21-hydroxylase. It is generally passed on in a pattern where a child inherits a changed gene from each parent, who may be unaffected carriers. The severity depends on how much enzyme activity remains. Because it is inherited, CAH is present from birth rather than acquired later, and a clinician may discuss family and genetic implications.

How it is diagnosed

Diagnosis relies on hormone tests that reveal the pattern of adrenal hormone production, sometimes supported by genetic testing. A clinician interprets the results together with the clinical picture. Common evaluations include:

• Hormone blood tests — including markers that build up when a particular enzyme is reduced, along with cortisol and androgens. See the cortisol test guide.
• Newborn screening — in regions where it is offered, this can flag more severe forms early.
• Stimulation testing — measuring how hormone levels respond to a stimulating signal, used in some cases.
• Genetic testing — to confirm the specific change and inform family planning, where appropriate.
• Salt and fluid checks — blood tests of the body's salts, important in forms that affect aldosterone.

The table below gives illustrative reference points only; actual ranges vary by laboratory, age, and the specific test, so results should be interpreted with a clinician.

These entries are illustrative and not diagnostic cut-offs. For background on the markers, see our blood tests section.

How it is generally managed

CAH is generally managed long term by an endocrinology team, with the goal of replacing the hormones the body cannot make in sufficient amounts and supporting healthy growth and development. The plan is highly individual and decided with a clinician. General elements often include:

• Replacing missing hormones — addressing low cortisol, and aldosterone where affected; details are individual and decided with a clinician.
• Monitoring growth and development — particularly important in children.
• Illness and stress planning — because the body's cortisol response is affected, a clinician explains an individual plan for times of illness or stress.
• Regular review — periodic checks of hormones and overall health, adjusting the plan as needs change.
• Family and genetic counselling — offered where appropriate, given the inherited nature.

General treatment principles are outlined in our treatments section, and related early-life and developmental topics in our life stages section. This page is educational and is not a substitute for personalised medical advice, and it does not describe doses or specific regimens.

Established understanding versus ongoing research

The core picture — an inherited enzyme change reducing cortisol, the diversion toward androgens, and the value of lifelong specialist care — is well established. Other areas, including the best long-term management strategies and outcomes for milder forms, remain active topics of study. Where evidence is still developing, decisions are best made with a clinician.